http://arxiv.org/abs/1402.0508
Measurement of the HI 21-cm power spectrum from the reionization epoch will be influenced by the evolution of the signal along the line-of-sight direction of any observed 3D volume. We use numerical and semi-numerical simulations to study this so-called light cone effect on the HI 21-cm power spectrum. We find that the light cone effect has the largest impact at two different stages of reionization: one when reionization is ~20% and other when it is ~80% completed. We find a factor of ~4 amplification of the power spectrum at the largest scale available for a line-of-sight extent of 607 Mpc. We do not find any significant anisotropy in the 21-cm power spectrum due to the light cone effect for Fourier modes that are observable with a radio interferometer. We argue that for the power spectrum to become anisotropic, the light cone effect would have to make the ionized bubbles significantly elongated or compressed along the line-of-sight, which would require extreme reionization scenarios. We also calculate the two-point correlation functions and find them to differ parallel and perpendicular to the line-of-sight. Finally, we calculate an optimum frequency bandwidth below which the light cone effect can be neglected when extracting power spectra from redshifted 21-cm observations. We find that if one is willing to accept a 10 % error due to the light cone effect, the optimum frequency bandwidth for k= 0.056 Mpc^-1 is ~7.5 MHz. For k = 0.15 and 0.41 Mpc^-1 the optimum bandwidth is ~11 and ~16 MHz respectively.
Wed, 5 Feb 14
15/61
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